1. Field of the Invention
The present invention relates to a control apparatus in a feed driving system to be used in industrial robots, machine tools, and post-machining deburring machines.
2. Description of the Related Art
A parallel kinematic machine is one type of mechanism for driving a movable body by an actuator and driving and controlling the movable body to a free position and orientation with respect to a holding base. A known machine tool equipped with a spindle head 2, which is a body that is freely movable in six axial directions in a machining space, is shown in FIG. 19 as an apparatus of the prior art employing the parallel kinematic machine. In this machine tool, six universal joints 5 are respectively disposed on a holding base 7. A servo motor 6a, which supports the top end of a ball screw 4 at each universal joint 5 and is a rotary actuator for driving the ball screw 4, is installed. As shown in FIG. 20, a position detector 6b is mounted to each motor 6a. 
The spindle head 2 is supported via the universal joint 3 at the bottom ends of the six ball screws 4 and a main spindle 8 is disposed at the spindle head so as to be pivotable. Then, by changing the position of the ball screws 4 between universal joints 3 and the universal joints 5, the arm lengths are changed and the spindle head 2 is positioned at an arbitrary orientation in the machining space and a workpiece on a table 1 is machined by a tool mounted to the main spindle 8. To the spindle head 2 are connected electrical wiring, such as electric supply lines and control signal lines for a main spindle drive motor, and piping for supplying fluids, such as pressurized oil for tool clamps, lubricating oil for bearings, and cooling water or cutting water. These wiring and piping are passed through a flexible tube 9 with leeway provided from the holding base 7 to the flexible tube 9.
A parallel kinematic machine tool performs feedback control independently at each of the 6 axes by utilizing the output from a position detector that is mounted to each servo motor. Control parameters for the servo system are .adjusted so that maximum feed velocity is obtained in the Cartesian coordinate system at various positions and orientations within the movable range. However, in the apparatus of the prior art, the same and fixed control parameters are used among the 6 axes.